[Pw_forum] About maximally localized wannier function

[Silviu Zilberman]

Sorry, after reading again your email I reallized that you did answer my 
question.

Thanks, Silviu.

Silviu Zilberman wrote:

> Dear Nicola,
>
> Thank you for your detailed explanation. Following on your last point, 
> suppose you do the best k-point sampling with PW, to obtain the total 
> charge density. One could impose this charge density in the CP 
> calculation, at every step, to get MLWF at the gamma-point that are 
> consistent with this charge density. Wouldn't it implicitly be 
> equivalent to the MLWF obtained in the full k-points optimization?
>
> Thanks, Silviu.
>
> Nicola Marzari wrote:
>
>>
>>
>> Dear Silviu,
>>
>> this is an interesting suggestion. The good thing about the
>> Gamma-sampling CP code algorithm is that it will always lead to
>> the true minimum of the localization functional, as long as a
>> cubic/tetragonal/orthorombic cells are used (i.e. derivatives are
>> calculated with 3 orthogonal G vectors). Depending on your application,
>> this could be very important or irrelevant - the more the system is 
>> large and disordered, the more it becomes useful/essential.
>> Another advantage is that the CP/Wannier subroutines work with ultrasoft
>> pseudopotentials, although this capability is forthcoming in 
>> wannier-transport.org and wannier.org .
>>
>> The regular k-point wannier codes use instead trial projection orbitals
>> (very straightforward  ones - usually one specifies the center of a
>> gaussian, and the l,m of a spherical harmonics) to start the 
>> minimization already in the right basin of attraction. This
>> approach works again very well in most cases - to the point that some 
>> groups just use these projections, without localization, to get
>> localized WFs (I think, e.g., Pickett's group).
>>
>> As a last note - if you use CP, your sampling can be "poor" if you have
>> a smallish unit cell. On the other hand, if you use PWSCF to feed CP,
>> you can make your charge density as good as you want it, sampling-wise.
>> Then, the only finite-size errors remaining will be on the calculation
>> of the MLWFs themselves, that, using CP, will only combine states
>> obtained at Gamma, instead of using all the Brillouin zone.
>>
>>                 nicola
>>
>>
>> Silviu Zilberman wrote:
>>
>>> Dear Xianghjun,
>>>
>>> MLWF are implemented in the CP code. I believe that the latest cvs 
>>> version has compatible restart files, which means you could use any 
>>> PWSCF calculation result as an input to a CP Wannier calculation. 
>>> This compatibility has only been introduced recently, and it may 
>>> still be unstable. You could also take the geometry from your PW 
>>> calculation and start a CP calculation from scratch and minimize the 
>>> wavefunction using Wannier dynamics. Look at the INPUT_CP file for 
>>> more details, as well as example #23.
>>>
>>> Silviu.
>>>
>>> xianghjun wrote:
>>>
>>>> Dear all,
>>>>  I am trying to get MLWF for some systems and want to know if MLWF 
>>>> has been implemented in PWSCF.
>>>> Thanks in advance.
>>>>
>>>> Best regards,
>>>> xianghjun
>>>>
>>>> =============================================================
>>>> H. J. Xiang
>>>> Ph.D. Candidate,
>>>> Hefei National Laboratory For Physical Sciences at Microscale,
>>>> University of Science and Technology of China,
>>>> Hefei, Anhui, 230026,
>>>> People's Republic of China
>>>> Tel.: 86-551-3606428
>>>> Fax.: 86-551-3602969
>>>> E-mail: xhongjun at mail.ustc.edu.cn
>>>> =============================================================
>>>>
>>>> _______________________________________________
>>>> Pw_forum mailing list
>>>> Pw_forum at pwscf.org
>>>> http://www.democritos.it/mailman/listinfo/pw_forum
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
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>>
>>
>>
>
>


-- 
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Zilberman Silviu
 
213 Frick Laboratory, Department of Chemistry 
Princeton University
Princeton, NJ 08544
 
phone: 609-258-1834
fax:   609-258-6746
silviu at Princeton.EDU
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